1. Technical Field
This invention relates generally to internal combustion engines, and more particularly to pistons for heavy duty diesel engines.
2. Related Art
It is known that internal combustion engines, and particularly diesel engines, experience high oil consumption that leads to undesirable exhaust emissions. In addition, with the oil consumption comes carbon build-up on surfaces of pistons, particularly in the top land area, including in the annular ring grooves. As such, the ring movements can be restricted by the carbon build-up, thereby diminishing the effectiveness of the rings to properly seal the combustion gas and control oil consumption, thereby resulting in increased oil blow-by, reduced engine performance, reduced engine component life, and increased emissions.
In addition to the problems mentioned above, an additional known problem can result from a non-uniform, turbulent flow of oil within the cylinder over the path of piston reciprocation. Some of these additional problems include the onset of liner cavitation and increased friction between the piston and the cylinder liner. The liner cavitation is sensitive to the configuration of the piston, particularly where the piston is of a monobloc construction having a fixed skirt formed as one piece with the piston. The increased friction is sensitive to secondary movements of the piston, where, for the lack of guidance, the piston reciprocates cocked within the cylinder liner. Oil control loss can be traced to the high velocity of piston travel, generating a standing wave of oil. If such is the case in the upper portion of the skirt, it results in a phenomenon referred to as “oil flooding”. As such, the majority of the oil is maintained toward the upper crown of the piston, and oil trickles into the ring belt area. In some cases, such as when the gas pressure gradient across the ring belt is not clearly defined, the first ring groove floods, whereupon the oil consumption control characteristic is lost. A secondary standing wave of oil forms at the upper edge of the first ring groove. Exposure of this oil to the flame front decomposes and carbonizes the oil in the standing wave, generating soot and formation of carbon deposits. As such, although it is desirable to maintain a continual supply of oil in the ring area of a piston, too much can be detrimental to the life of the engine and can also reduce the engine performance.
A piston manufactured according to the present invention and engine therewith overcomes or greatly minimizes the drawbacks resulting from at least those problems discussed above, thereby allowing diesel engines to operate at an increased performance level, while reducing their fuel consumption, oil consumption and exhaust emissions, besides prolonging their useful life.